Method and apparatus for testing a semiconductor device

ABSTRACT

The present disclosure provides methods for testing and evaluating electrical parameters of electronic circuits. An exemplary method includes providing a device-under-test electrically coupled to a testing apparatus; and determining an optimum value of a first electrical parameter and an optimum value of a second parameter by testing the device-under-test according to a set of first electrical parameter values and a set of second electrical parameter values. The optimum value of the first electrical parameter and the optimum value of the second parameter are determined based on an electrical noise response of the device-under-test.

This application is a divisional application of U.S. patent applicationSer. No. 13/225,816, filed Sep. 6, 2011, now U.S. Pat. No. 9,459,316,the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs.

The fabrication of semiconductor devices may involve one or more testingprocesses. A plurality of test units and test pads may be used to carryout the testing. For traditional testing methods, the available numberof test units is constrained by the available number of test pads. Assemiconductor device continue to shrink, available space on a waferbecomes a valuable resource. As a result, the number of test pads on thewafer may be limited (e.g., less than 30) due to chip area consumptionconcerns, and that in turn limits the number of test units that can beimplemented. As IC technologies continue to advance, the limited numberof test units and test pads may not be sufficient to allow effective andefficient execution of the testing processes. Furthermore, electricalnoise such as parasitical leakage may also adversely affect testmeasurement accuracy.

Therefore, while existing testing apparatuses and methodologies aregenerally adequate for their intended purposes, they have not beenentirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A-1B are diagrammatic views of certain structures used for wafertesting.

FIG. 2 is a diagrammatic view of a testing apparatus according tovarious aspects of the present disclosure.

FIG. 3 is a diagrammatic view of a testing pad and a plurality ofswitching devices coupled thereto.

FIGS. 4A-4C are diagrammatic views of example switching devices.

FIGS. 5A-5B are diagrammatic views of example testing units.

FIG. 6 is a diagrammatic view of a control circuit, the testing pads,the testing units, and the switching devices.

FIG. 7 is a diagrammatic view of a testing apparatus that includes thecontrol circuit, the testing pads, the testing units, and the switchingdevices.

FIG. 8 is a diagrammatic top view of the testing apparatus that includesthe control circuit, the testing pads, the testing units, and theswitching devices.

FIG. 9 is a flowchart illustrating a method for testing a waferaccording to various aspects of the present disclosure.

FIG. 10 is a circuit diagram illustrating a semiconductor testingcompensation scheme.

FIGS. 11A-11C are circuit diagrams illustrating one or more switchingdevices.

FIG. 11D is a graph illustrating a relationship between leakage currentand supply voltage.

FIG. 12 is a flowchart illustrating a method of testing a semiconductordevice according to various aspects of the present disclosure.

FIG. 13 is a three-dimensional graph illustrating a relationship betweenleakage current and supply voltage and device terminal voltage.

FIG. 14 is a two-dimensional graph illustrating a top view of thethree-dimensional graph of FIG. 13.

FIGS. 15A and 15B are plots of signal-to-noise (S/N) ratio performancesassociated with different testing methods, respectively.

FIG. 16 is a flowchart illustrating a method for testing a waferaccording to various aspects of the present disclosure.

FIG. 17 is a block diagram of a computer system for performing the stepsof the methods illustrated in FIGS. 9, 12, and 16.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the formation of a first feature over or on a second feature in thedescription that follows may include embodiments in which the first andsecond features are formed in direct contact, and may also includeembodiments in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. Various features may be arbitrarily drawn indifferent scales for simplicity and clarity.

FIGS. 1A and 1B are circuit diagrammatic views of two example testingapparatuses for testing a semiconductor wafer. FIG. 1A illustrates atesting apparatus 40, which includes a plurality of testing units 50(also referred to as test structures or device under test (DUT)) whosevarious terminals are each coupled to a respective one of a plurality oftesting pads 60. The testing units 50 are designed and implemented forthe electrical testing of a semiconductor circuit element or component,such as a transistor or a resistor. Thus, the testing units 50 may eachcontain one of the semiconductor elements or components. The testingpads 60 are conductive pads for establishing electrical connectionsbetween the terminals of the testing units 50 and external devices.Electrical currents or voltages may be applied to the testing pads 60.

FIG. 1B illustrates a testing apparatus 70, which includes a pluralityof testing units 80 and a plurality of testing pads 90. The testingunits 80 and the testing pads 90 are coupled together by a decoder 95.The decoder 95 may contain a multiplexer, inverters, and/or Booleanlogic gates such as AND, OR, NAND, NOR, XOR gates. The decoder 95 isoperable to establish electrical connections between one or more of thetesting units 80 and the testing pads 90.

A limitation of the testing apparatus 40 of FIG. 1A and the testingapparatus 70 of FIG. 1B is that they require too many testing pads 60.For instance, for the testing apparatus 40, twenty-one testing pads areused to effectively test eight testing units. Testing pads consume areaon the wafer, which has become an increasingly valuable resource as thechip scaling down process continues. Therefore, having an excessivenumber of testing pads wastes resources. The testing apparatus 70requires fewer testing pads than the testing apparatus 40. In general,the testing apparatus 70 can support X number of testing units with Ynumber of testing pads, where X=2{circumflex over ( )}Y. However, thismeans that as the number of testing units increase, the number oftesting pads still increases, even if the increase is not in a linearmanner. Modern semiconductor fabrication may require an ever largernumber of testing units to effectively test the performance of thewafer. Thus, the testing apparatus 70 may not be able to handle thedemands of modern semiconductor fabrication, because it may not be ableto supply enough testing pads (to support the number of the testingunits required by modern semiconductor fabrication).

To address these shortcomings discussed above, the present disclosureimplements a testing apparatus that utilizes a control circuit and aswitching circuit to select desired testing units. Referring to FIG. 2,a simplified block diagram of a testing apparatus 100 is illustrated.The testing apparatus includes a plurality of testing pads representedby block 110, a plurality of testing units (also referred to as teststructures) represented by block 120, a switching circuit/circuitry 130(also referred to as routing circuit/circuitry), and a controlcircuit/circuitry 140.

The testing pads 110 include a plurality of conductive testing pads,through each of which a test signal can be applied. The test signal maybe an electrical current or an electrical voltage. The testing units 120include a plurality of test units that are designed and implemented forthe testing of semiconductor circuit elements or components. Forexample, a testing unit may include an active device such as atransistor (e.g., field-effect transistor FET or bipolar junctiontransistor BJT) or a passive device such as a resistor, capacitor, orinductor. Each of the testing units 120 includes one or more terminalsfor electrically coupling with other devices.

The testing pads 110 and the testing units 120 are coupled together bythe switching circuit 130. The switching circuit 130 contains aplurality of switching devices that can be selectively activated anddeactivated (turned on and off, or closed and opened). The switchingdevices are each coupled to a respective one of the terminals of thetesting units. The operation of the switching circuit 130 iselectrically coupled to and controlled by the control circuit 140. Thecontrol circuit 140 includes devices that can selectively activate theswitching devices. In an embodiment, the control circuit 140 includes aplurality of flip-flop devices as the control devices. The testing pads110, the testing units 120, the switching circuit 130, and the controlcircuit 140 are discussed below in more detail.

FIG. 3 illustrates a simplified circuit diagrammatic view of a testingpad 110 and a plurality of switching devices 200 coupled thereto. Thetesting pad 110 includes a conductive material, for example copper oraluminum. An electrical signal (for example, a test signal) can beapplied to the testing apparatus disclosed herein through the testingpad 110. A commonly used testing WAT testing pad size is 50 microns(um)×50 um in a 60 um height scribe line, pad pitch 100 um and pad space50 um; in general, pad number in a WAT test line is more than 20. It isunderstood that alternative sizes and dimensions of the testing pads andscribe lines may be employed for various optimization considerations.

As is illustrated, the testing pad 110 is coupled to a plurality ofswitching devices 200. The switching devices 200 are switching devicesof the switching circuit 130 of FIG. 2. Each switching device can beselectively activated to let an electrical signal pass through, ordeactivated to let no electrical signal pass through. Although notillustrated for the sake of simplicity, it is understood that thetesting apparatus of the present disclosure includes a plurality ofadditional testing pads similar to the testing pad 110, wherein thesetesting pads are each coupled to a plurality of switching devicessimilar to the switching devices 200 of FIG. 3.

FIGS. 4A-4B illustrate simplified circuit diagrams of differentembodiments of the switching devices 200 of FIG. 3. In FIG. 4A, aswitching device 200A includes a transmission gate. The transmissiongate is implemented with a parallel combination of an NMOS transistorand a PMOS transistor. The signal at the gate of the NMOS transistor iscomplementary to the input at the gate of the PMOS transistor, or viceversa. For example, if a logical high (1) is applied at the gate of theNMOS transistor, then a logical low (0) is applied at the gate of thePMOS transistor. In an embodiment, the PMOS transistor has a largerwidth than the NMOS transistor, since the PMOS transistor has a lowermobility.

The switching device 200A has input/output terminals 201-202 and controlterminals 203-204. A data signal can be sent through the input/outputterminals 201-202 and pass through the switching device 200A withnegligible signal loss. A control signal can be applied to the controlterminals 203-204. The control signal determines whether the switchingdevice 200A is activated (turned on) or deactivated (off). In thismanner, the switching device 200A serves as a bidirectional tunableswitch—data signal can travel from the terminal 201 to the terminal 202or from the terminal 202 to the terminal 201.

In FIG. 4B, a switching device 200B includes a PMOS pass gate. The PMOSpass gate is implemented using a PMOS transistor device. Similar to thetransmission gate in FIG. 4A, the PMOS pass gate has input/outputterminals 211-212 through which a data signal can be applied, and acontrol terminal 213 through which a control signal can be applied toactivate or deactivate the PMOS pass gate. In FIG. 4C, a switchingdevice 200C includes an NMOS pass gate. The NMOS pass gate isimplemented using an NMOS transistor device. Similar to the transmissiongate in FIG. 4A, the NMOS pass gate has input/output terminals 221-222through which a data signal can be applied, and a control terminal 223through which a control signal can be applied to activate or deactivatethe NMOS pass gate. It is understood that the switching devices200A-200C shown in FIGS. 4A-4C are merely examples, and that othersuitable switching devices may be employed in alternative embodiments.

FIGS. 5A-5B include simplified circuit diagrams of example testing unitsthat are embodiments of the testing units 120 shown in FIG. 2. In FIG.5A, a testing unit 120A contains a transistor device, for example a FETtransistor device. The transistor device has a gate terminal, a sourceterminal, a drain terminal, and a body terminal. Each of these terminalsis coupled to two switching devices 200 (where the switching devices 200may be implemented according to one of the embodiments shown in FIGS.4A-4C or another suitable implementation). For each terminal of thetransistor device, one of the switching devices 200 is used to force asignal (for example, an electrical current) to the terminal, and theother one of the switching devices 200 is used to sense a signal (forexample, an electrical voltage) at the terminal. This type offorcing-sensing scheme can be used to compensate for circuit parasiticssuch as parasitic resistance.

In FIG. 5B, a testing unit 120B contains a resistor device. The resistordevice has two terminals, each one of which is also coupled to twoswitching devices 200. Similar to the case in the testing unit 120A, oneof the switching devices 200 can be used to force a current to aterminal of the testing unit 120B, while the other one of the switches200 can be used to sense a voltage at that terminal. Each of theswitches 200 of the testing units 120A and 120B is coupled to arespective one of the testing pads 110 shown in FIGS. 2-3. Theforcing-sensing aspect of the testing according to the presentdisclosure will be discussed below in more detail with reference toFIGS. 10-12.

It is understood that the testing units of the testing apparatusdisclosed herein may have different implementations or configurationsthan what has been illustrated. For example, some testing units may onlyhave a subset of their terminals coupled to switching devices, while theother terminals are left open or are grounded. As another example, sometesting units may only have one or more terminals that are each coupledto one switching device instead of to two switching devices. For thesake of simplicity, these additional testing units are not illustratedherein.

FIG. 6 illustrates a simplified fragmentary circuit diagram of anembodiment of the control circuit 140 of FIG. 2. The control circuit 140contains a plurality of storage elements, some of which are illustratedherein as storage elements 300-304. The storage elements 300-304 canstore a state, such as a logical high (1) state or a logical low (0)state. In the embodiment shown, the storage elements 300-304 areimplemented with D (data) flip-flop devices. Therefore, the storageelements 300-304 may also be referred to as flip-flop deviceshereinafter. These flip-flop devices each have a D (data) input, a CLK(clock) input, an R (reset) input, a Q output, and a QB output (oppositeof the Q output).

The flip-flop devices 300-304 are coupled together in series. Theflip-flop device 300 has its D input coupled to a signal source 320,which outputs a logic high signal (1) in the present embodiment. Forexample, the signal source 320 may be tied to a power-rail such as Vddor Vss. The QB output of the flip-flop device 300 is coupled to the Dinput of the flip-flop device 301, but for the rest of the flip-flopdevices 301-304, each preceding flip-flop device has its Q outputcoupled to the D input of the subsequent flip-flop device. As anexample, the flip-flop device 301 (the preceding flip-flop device inthis example) has its Q output coupled to the D input of the flip-flopdevice 302 (the subsequent flip-flop device in this example).

The flip-flop devices 300-304 also each have their R input coupled to areset signal 330. When the reset signal 330 is actuated, all theflip-flop devices 300-304 are reset. The flip-flop devices 300-304 alsoeach have their CLK input coupled to a clock signal 340. A plurality ofbuffers 350-353 are used to buffer the clock signal 340 before the clocksignal is received by the CLK input of the flip-flop devices 300-303.

The Q outputs of flip-flop devices 301-304 are coupled to switchingdevices 200A-200D, respectively. The switching devices 200A-200D arerespectively coupled between testing units 120A-120D and a subset oftesting pads 110. In other words, the testing units 120A-120D “share”the subset of testing pads 110, but not at the same time. Electricalconnections may be established between the subset of the testing pads110 and a particular one of the testing units 120A-120D if the switchingdevices for that testing unit are activated.

For example, electrical connections may be established between thetesting pads 110 and the testing unit 120A if the switching devices 200Aare activated (turned on) while the switching devices 200B-200D aredeactivated (turned off). Meanwhile, since the switching devices200B-200D are deactivated, no electrical connections are establishedbetween the testing units 120B-120D and the testing pads 110. It isunderstood that if the switching devices are transmission gates, aninverter may also be coupled to the Q output of the respective flip-flopdevice, so that logically-complementary control signals may be providedto the transmission gates from that flip-flop device.

The flip-flop devices 301-304 disclosed herein are configured to turn onone set of switching devices at a time (according to clock pulses), soas to activate only one testing unit at any given time. Thus, electricalconnections between that testing unit and at least a subset of testingpads is established, while no electrical connections exist between therest of the testing units and that subset of testing pads.

In more detail, at each pulse of the clock signal 340, one of theflip-flop devices outputs a logical high control signal at its Q output.For example, the flip-flop device 301 outputs a logical high controlsignal at its Q output. This logical high control signal activates theswitching devices 200A, which allows the testing unit 120A to beelectrically coupled to the testing pads 110. Meanwhile, the otherflip-flop devices 302-304 output a logical low during this clock pulse,which means that the switching devices 200B-200D are turned off.Consequently, testing units 120B-120D are not activated and have noelectrical connections with the testing pads 110 at this time.

At the next clock pulse, the flip-flop device 302 outputs a logical highand activates the switching devices 200B. This allows electricalconnections to be established between the testing unit 120B and thetesting pads 110. Meanwhile, the flip-flop devices 301 and 303-304output a logical low and deactivates the switching devices 200A and200C-200D. Thus, no electrical connections exist between the testingpads 110 and the testing units 120A and 120C-120D.

In this manner, at each clock pulse, a different one of the testingunits is activated (through the set of switching devices coupledthereto) and is allowed access to the testing pads 110. Electricaltesting may be done to that testing unit at that time by applyingtesting signals through the testing pads. This configuration allows thenumber of testing pads to remain at a fixable low number, even as thenumber of testing units increases.

It is understood that a plurality of additional flip-flop devices (andthe corresponding switching devices and testing units) exist between theflip-flop devices 303 and 304, but they are not illustrated herein forthe sake of simplicity. It is also understood that in alternativeembodiments, other suitable digital circuit devices may be used toimplement the storage elements 300-304, for example SR (set-reset)flip-flops, JK flip-flops, or latches.

FIG. 7 is a fragmentary circuit diagrammatic view of the testingapparatus 100 of FIG. 2. The testing apparatus 100 includes the testingpads 110, the testing units 120, the switching circuit 130, and thecontrol circuit 140. A subset of the testing pads 110 is shown. In anembodiment, the testing pads 110 include eight testing pads for couplingto the four terminals of a transistor device (two testing pads for eachterminal, i.e., one testing pad for forcing a current, another testingpad for sensing a voltage), one testing pad for the application of theVdd signal, one testing pad for the application of the Vss signal, onetesting pad for the application of the clock signal, and one testing padfor the application of the reset signal. Thus, a total of twelve testingpads are used in that embodiment. It is understood that other number oftesting pads may be employed in alternative embodiments.

For the sake of simplicity, only two of the testing units are shown inFIG. 7 as testing units 120A and 120B, which contain FET transistordevices. The four terminals (gate, source, drain, body/bulk) of each FETtransistor device are each coupled to two the testing pads 110 throughtwo respective switching devices. The switching circuit 130 contains aplurality of such switching devices, which may be implemented usingtransmission gates, PMOS pass gates, or NMOS pass gates, as discussedabove. The operation (opening or closing) of the switching devices arecontrolled by the control circuit 140, which contains a plurality ofstorage elements such as D flip-flops.

As discussed above with reference to FIG. 6, at each clock pulse, arespective subset of the switching devices is activated so as to enableelectrical coupling between one of the testing units (such as thetesting unit 120A) and at least a subset of the testing pads 110. Thus,each testing unit may be tested using the same set of testing pads 110without causing electrical shorting. Stated differently, a plurality oftesting units may “share” a common set of testing pads, but in atime-divided manner. At any given point in time, only one testing unithas access to the testing pads 110.

FIG. 8 is a simplified diagrammatic top level view of the testingapparatus 100 (of FIG. 2). In an embodiment, the testing apparatus 100is implemented in a scribe line region of a wafer. The scribe lineregion includes regions between rows or columns of IC devices. Wafercutting may take place in the scribe line region. The testing apparatus100 may also be referred to as a test line. The testing apparatus 100includes a plurality of testing pads 110. In an embodiment, there aretwelve testing pads: four testing pads for signals Vdd, Vss, CLOCK, andRESET, eight testing pads for the four terminals of a transistor device(two testing pads for each terminal). The testing apparatus 100 includesa plurality of testing units 120, for example hundreds or thousands ortesting units. The testing pads 110 may have dimensions that aresignificantly larger than the dimensions of the testing units. Thetesting pads 110 and the testing units 120 may at least partiallyoverlap.

The testing apparatus 100 also contains circuitry 400. The circuitry 400includes the switching circuit 130 of FIG. 2, as well as the controlcircuit 140 of FIG. 2. The switching circuit 130 contains controllableswitching devices coupled between the testing pads 110 and the testingunits 120. As discussed above, the control circuit 140 contains storageelements such as flip-flop devices that can control the operation of theswitching devices so as to control which testing unit can haveelectrical access to the testing pads 120. The dimensions of eachtesting pad may also be significantly larger than the individualswitching devices and/or flip-flop devices.

Illustrate in FIG. 9 is a flowchart of a method 500 for testing asemiconductor device according to various aspects of the presentdisclosure. It is also understood additional processes may be providedbefore, during, and after the method 500 of FIG. 9, and that some otherprocesses may only be briefly described herein.

Referring to FIG. 9, the method 500 begins with block 510 in which aplurality of testing pads is provided. The method 500 continues withblock 520 in which a plurality of testing units is provided. The method500 continues with block 530 in which a plurality of controllableswitching devices is provided. The switching devices are each coupledbetween a respective one of the testing pads and a respective one of thetesting units. The method 500 continues with block 540 in which a subsetof the switching devices is selectively activated. The subset of theswitching devices is all coupled between a selected one of the testingunits and at least a subset of the testing pads. The execution of block540 establishes electrical coupling between the selected testing unitand the subset of the testing pads.

Recall from the discussions above in association with FIGS. 5A-5B, twoswitching devices (or two testing pads) may be used for each terminal ofa testing unit, one for forcing a current, the other one for sensing avoltage. This forcing-sensing scheme is implemented to compensate forelectrical parasitics such as an IR voltage drop. Referring to FIG. 10,a circuit diagram of an example forcing-scheme is illustrated. A testcurrent I is applied through a testing pad 110A (also referred to as aforce pad). The test current I goes through switching device 200A beforereaching a terminal of a testing unit (not illustrated). As an example,the testing unit may be a FET transistor, and the terminal coupled tothe switching device 200A may be its drain terminal. Thus, a drainvoltage “VD” is present at the drain terminal of the FET transistor.

It may be desired that the drain voltage VD is at a certain level, forexample 0.9 volts (V). Circuit parasitics may affect the precision andaccuracy of the drain voltage VD. Therefore, a feedback loop is createdby a switching device 200B and a testing pad 110B (also referred to as asense pad) coupled thereto. The testing pad 110B senses the voltage VDat the drain terminal. The difference between the sensed drain voltageand the desired drain voltage may be fed back to a control circuit (notillustrated in FIG. 10), which may be implemented within or separatelyfrom the control circuit 140 of FIG. 2. The control circuit can adjustthe test current I (either adjusting it upwards or downwards) until thesensed drain voltage is substantially equal to the desired drainvoltage. In this manner, the parasitic effects may be substantiallycompensated.

However, background electrical noise may still present a problem incertain situations. Especially for those small current test items suchas Ioff, Ig, Ib and Vt, whose desired current level are around nano-Ampor pico-amp levels. For example, referring to FIG. 3, undesired leakagecurrent may be produced by one or more of the switching devices 200and/or the control circuit 130 of FIG. 2 (containing flip-flop devices).Leakage current may be generated by the switching devices even when theyare deactivated. Since each testing pad 110 is coupled to a plurality ofswitching devices 200, as is shown in FIG. 3, the cumulative amount ofleakage current may not be ignored, cumulative leakage current may causea low S/N (signal/noise) ratio, for example, (test unit Ioff)/(switchdevices background leakage)<100X. Therefore, the accurate test unitcurrent measurement needs to minimize the background current to resultin a S/N ratio greater than 100X.

The paragraphs below will discuss an approach to minimize the harmfuleffects of electrical noise such as leakage current. FIG. 11Aillustrates a circuit diagrammatic view of a plurality of switchingdevices 200 that are coupled in parallel to a testing pad 110. Theswitching devices 200 are implemented as transmission gates in FIG. 11A.The switching devices 200 herein are switched off (deactivated) butstill produce undesired leakage current, which can be measured as “Id”by the testing pad 110. Flip-flop devices of the control circuit thatcontrols the operation of the switching devices 200 may also contributeto the leakage current.

FIG. 11B is a circuit diagrammatic view of one of the switching devices200. In more detail, two complementary (NFET and PFET) transistordevices are electrically coupled by having their respective source anddrain terminals tied together. The input and output of the switchingdevice are taken from the source and drain terminals. The gates of theFET transistors serve as control terminals, which are coupled to theflip-flop devices of the control circuit (not illustrated herein for thesake of simplicity) in a manner described above with reference to FIGS.6-7. The body or substrate terminal of the PFET transistor is tied to apower supply voltage “VDD”, and the body or substrate terminal of theNFET transistor is tied to “VSS” serving as electrical ground.

FIG. 11C is an equivalent circuit diagrammatic view of the switchingdevice illustrated in FIG. 11B. Namely, the NFET and PFET transistorscan be modeled as diodes. The diode equivalent to the PFET transistorsources a leakage current onto the input terminal, and the diodeequivalent to the NFET transistor sinks a leakage current from the inputterminal. In other words, the direction of the leakage current flows ofthe PFET and NFET transistors are opposite: a leakage current flows outof the PFET transistor (and into the input terminal), whereas a leakagecurrent flows into the NPFET transistor (from the input terminal).Another way of viewing this is that the leakage currents produced by thePFET and NFET transistors have opposite polarities: one is positive, theother one is negative.

Since the total amount of leakage current is a sum of the PFETtransistor leakage current and the NFET transistor leakage current, thetotal leakage can be minimized if the PFET and NFET transistor leakagecurrents are manipulated to cancel each other out. One way to manipulatethe PFET and NFET transistor leakage currents is through a sweeping of asupply voltage. This is at least in part due to the fact that aparticular supply voltage will affect the PFET transistor leakagecurrent differently than it does the NFET transistor leakage current.Stated differently, as the supply voltage is adjusted, different amountsof PFET and NFET leakage currents may be obtained.

Referring to FIG. 11D, a graph 700 illustrates a relationship between asupply voltage and the total amount of leakage current. In theembodiment shown, the X-axis of the graph 600 represents the supplyvoltage, which is VDD. The Y-axis of the graph 600 represents theleakage current, which is the total amount of leakage current Idmeasured by the testing pad 110. Thus, the leakage current Id is thecumulative leakage current generated by all the electronic circuitry(including the switching devices and the flip-flop devices) coupled tothe testing pad 110.

As is illustrated in FIG. 11D, the total leakage current changes as thesupply voltage is swept along the X-axis. For example, when the supplyvoltage VDD is 1.5 V, the total leakage current is about 10 nano-amps(nA). As the supply voltage increases, the total leakage current beginsto drop. When the supply voltage is at or near 1.9 V, the total leakagecurrent is minimized, which is about 0.1 pico-amps (pA). After that, asthe supply voltage increases, the leakage current begins to increaseonce again. For example, when the supply voltage is at about 2.2 V, thetotal leakage current is about 1 nA. Thus, in the embodiment illustratedin FIG. 11D, 1.9 V is an optimum value for the supply voltage VDD. Thisis because at VDD=1.9 V, the PFET leakage current and the NFET leakagecurrent substantially cancel each other out, thereby resulting in a lowoverall leakage current. It is understood that these specific valuesdiscussed herein merely serve as examples, and that a supply voltage mayhave different values in other embodiments.

According to an embodiment, the following steps are performed togenerate the chart 600. First, the flip-flop devices in the controlcircuit are reset, and all the switching devices are reset to be in anoff state. Second, a test signal is applied through the testing pad toforce a test voltage at a desired terminal of the testing unit. Third,the power supply voltage VDD of the control circuit and the switchingdevices is swept from a first value to a second value. Then an optimizedpower supply voltage VDD is obtained. The optimized power supply voltageVDD yields a minimum electrical background noise (e.g., a total amountof current leakage). Thereafter, the optimized power supply voltage VDDis adopted and used as the power supply voltage to power the flip-flopdevices and the switching devices. The subsequent electrical testing ofthe testing unit can be performed at a high accuracy.

FIG. 12 is a flowchart that illustrates a method 700 for testing asemiconductor device according to various aspects of the presentdisclosure. The method 700 includes block 710, in which a testing unitand an electronic circuit are provided. The electronic circuit includesat least one of: switching circuitry and control circuitry. Theelectronic circuit contains a plurality of circuit components, such astransmission gates, pass gates, and flip-flop devices. The electroniccircuit is coupled to the testing unit.

The method 700 includes block 720, in which a first electrical signal isapplied to the testing unit. In an embodiment, the first electricalsignal is a test voltage. In an embodiment, the block 720 includesforcing a voltage as the first electrical signal to a terminal of thetesting unit.

The method 700 includes block 730 in which a second electrical signal isswept across a range of values. In an embodiment, the second electricalsignal is a power supply voltage that supplies power to the electroniccircuit. The sweeping of the second electrical signal is performed whilea value of the first electrical signal remains substantially the same.

The method 700 includes block 740, in which a third electrical signal ismeasured during the sweeping of the second electrical signal. In anembodiment, the third electrical signal is a leakage current. Themeasured third electrical signal has a range of values that eachcorrespond to one of the values of the second electrical signal. In anembodiment, the steps in blocks 720, 730, and 740 are all performedwhile the circuit components in the electronic circuit are turned off.In an embodiment, the steps in blocks 730 and 740 are carried out in amanner such that a value of the third electrical signal is obtained ateach value of the second electrical signal.

The method 700 includes block 750, in which a value of the secondelectrical signal that yields a minimum value of the third electricalsignal is adopted as an optimum value of the second electrical signal.The method 700 includes block 760, in which the testing unit is testedwhile the second electrical signal is set to the optimum value. Thetesting is performed while at least a subset of the circuit componentsof the electronic circuit is turned on.

It is understood that in accordance with the method 700, a plurality oftesting pads and a plurality of additional testing units may beprovided. Each testing pad is coupled to the testing unit and theadditional testing units through the electronic circuit. The steps inthe method 700 may be performed through at least a subset of the testingpads.

Since the method 700 discussed above involves sweeping the power supplyvoltage VDD, it may be referred to as a one-dimensional sweepingprocess. This one-dimensional sweeping process is capable of finding theoptimum VDD to reduce current leakage noise in many applications.However, as process or device variations increase, the one-dimensionalsweeping process may not be sufficient to cover all leakage situations.In other words, an “optimum” VDD value obtained from performing theone-dimensional VDD sweep may not actually be the best VDD value tominimize leakage current. This problem may be exacerbated if paralleltesting is implemented, where multiple DUTs or testing units are testedconcurrently. To address these issues, a multi-dimensional sweepingprocess is proposed by the present disclosure and discussed in moredetail below.

Referring to FIG. 13, a three-dimensional graph 800 illustrates arelationship between leakage current, device terminal voltage, andsupply voltage. The X-axis of the graph 800 represents the supplyvoltage (also referred to as control circuit voltage), which is VDD inthe present embodiment. The Y-axis of the graph 800 represents theleakage current, which is the total amount of leakage current Idmeasured by the testing pad 110. Thus, the leakage current Id is thecumulative leakage current generated by all the electronic circuitry(including the switching devices and the flip-flop devices) coupled tothe testing pad 110. The Z-axis of the graph 800 represents the deviceterminal test voltage (also referred to as a force voltage, since thevoltage is “forced” onto a terminal of a testing unit or DUT).

The X-axis, Y-axis, and Z-axis are orthogonal or perpendicular to oneanother. A “cut” along the X-axis would result in a two-dimensionalplane defined by the X-axis and the Y-axis. The projection of thethree-dimensional graph on that two-dimensional graph would appear as agraph that resembles the graph 600 of FIG. 11D. This is because such cuteffectively uses a fixed device terminal voltage, which is how theone-dimensional sweep (sweeping supply voltage VDD along the X-axis)discussed above with reference to FIG. 11D is carried out.

However, it can be seen from graph 800 that the lowest leakage currentmay not necessarily be obtained by maintaining the device terminalvoltage at a random given value. Rather, the leakage current, the deviceterminal voltage, and the supply voltage are all interdependent. Inother words, leakage current varies in response to the device terminalvoltage as well as to the supply voltage. Hence, to obtain the lowestleakage current, a multi-dimensional sweeping process with respect tothe supply voltage and the device terminal voltage needs to beperformed.

Referring to FIG. 14, a two-dimensional graph 850 shows a top view ofthe graph 800 of FIG. 13. In other words, the graph 850 represents whatcan be observed by looking down along the Y-axis from the top of thegraph 800 of FIG. 13. Therefore, the graph 850 is located in a planethat is defined by an X-axis that is the supply voltage, and a Z-axisthat is the device terminal voltage. The graph 850 contains a curve 860that represents a target performance. In an embodiment, the curve 860represents the lowest amount of leakage current that can be obtained,which should be as close to zero as possible.

The graph 850 also contains curves 865, 870, 875, and 880. The curves860-880 represent four different process corners, respectively. In anembodiment, the curve 865 represents the process corner in which an NFETis slow and a PFET is slow (SS), the curve 870 represents the processcorner in which an NFET is slow and a PFET is fast (SF), the curve 875represents the process corner in which an NFET is fast and a PFET isslow (FS), and the curve 880 represents the process corner in which anNFET is fast and a PFET is fast (FF). The leakage performance of atesting unit should be bound within these four process corners.

A multi-dimensional sweeping process is performed by sweeping both thesupply voltage along the X-axis and the device terminal voltage alongthe Z-axis. Since there are two variables (supply voltage and deviceterminal voltage) in the embodiment illustrated, the multi-dimensionalsweeping process is a two-dimensional sweeping process. However, it isenvisioned that as more variables are involved, the multi-dimensionalsweeping process may be a three-dimensional, four-dimensional, or anyother dimensional sweeping process in alternative embodiments.

According to an embodiment, the multi-dimensional sweeping process iscarried out using a nested loop structure. In general, a nested loop isa logical structure where two repeating loops are placed in “nested”form, that is, an inner loop is situated within the body of an outerloop. Each iteration of the outer loop triggers the execution of theinner loop, which may contain a plurality of cycles. According to anembodiment of the present disclosure, the inner loop is the sweepingacross device terminal voltage, and the outer loop is the sweepingacross supply voltage. As such, the execution of the nested loopinvolves sweeping the device terminal voltage across a desired rangewhile the supply voltage is held at an initial value (i.e., theexecution of the inner loop), and thereafter repeating the sweeping ofthe device terminal voltage a plurality of times, wherein each time thevalue of the supply voltage is increased (i.e., this is the execution ofthe outer loop).

The inner loop and outer loop may each be executed any number of timesdepending on their step sizes. As the step sizes decrease, the loopswill be iterated more times. On the other hand, as the step sizesincrease, the loops will be iterated fewer times. In one embodiment,both the inner loop and outer loop are iterated using small step sizes,for example step sizes in the range of a few milli-volts (mV) orone-tenths of mV. This embodiment will yield a supply voltage and acorresponding device terminal voltage that are respectively very closein value to the true optimum supply voltage and device terminal voltagethat will result in the lowest leakage current possible. Hence, when atesting unit or DUT is tested using the supply voltage and the deviceterminal voltage obtained after executing the nested loop using smallstep sizes, a very low leakage current can be obtained. As such, thesupply voltage and device terminal voltage values obtained in thatembodiment may be practically considered to have optimum values.

However, one drawback of the embodiment discussed above is that it willtake a long time to execute the nested loop due to the small step sizes.As an example, if the sweeping range and the step size are 1 V and 1 mV,respectively, for both the supply voltage and the device terminalvoltage, it would take 1000×1000=1 million data samples (or measurementcycles) to complete the execution of the nested loop. The amount of timeit takes to complete such nested loop may not be suitable for certainapplications.

As a tradeoff, another embodiment (shown in FIG. 14) offers speedimprovements by performing a coarse sweeping process first to obtain theoptimum supply voltage, and thereafter performing a fine sweepingprocess to obtain the optimum device terminal voltage. In more detail,the coarse sweeping process involves executing the above-mentionednested loop in a manner similar to the embodiment discussed above,except both the inner loop and the outer loop now have relatively largestep sizes. In certain embodiments, the step sizes may be tens orhundreds of mVs. Consequently, the inner loop or the outer loop may eachcontain just a few iterations.

The coarse sweeping process yields a plurality of samples points 890,which are represented by the stars in graph 850. In other words, eachdata point (star) 890 is a result of an iteration of the nested loop andrepresents a leakage current obtained at a specific supply voltage and aspecific device terminal voltage. Since the step sizes are big, theinner loop contains four cycles, as does the outer loop in theembodiment shown herein. Consequently, the nested loop contains 4×4=16cycles or iterations, which can be performed quickly. But as a result ofthe big step sizes, the coarse sweeping process may very well miss the“sweet spot” of supply voltage and/or the device terminal voltagecorresponding to the lowest amount of leakage current. This is visuallyindicated by the fact that none of the data points 890 in the graph 850are located on the target curve 860. Therefore, the optimum value ofonly one of the two parameters (supply voltage and device terminalvoltage) is defined by the execution of the coarse sweeping process. Inan embodiment, the optimum supply voltage is defined by the execution ofthe coarse sweeping process. This supply voltage is obtained byidentifying the data point 890A that is located closest to the targetcurve 860. The supply voltage value associated with the data point 890Awill be recorded and fixed for the subsequent fine sweeping process.

Thereafter, a fine sweeping process is performed based using the datapoint 890A as a starting point. The fine sweeping process is performedwhile the supply voltage is held at the value associated with data point890A. Device terminal voltage is swept along a desired range (along theZ-axis) with a smaller step size than that associated with the coarsesweeping process. The fine sweeping process will yield a data point 895,which is located at an intersection between the target curve 860 and thevertical Z-axis on which the data point 890A is swung. Thus, the datapoint 895 has the same supply voltage value as the data point 890A. Thedevice terminal voltage associated with the data point 895 will berecorded as the optimum device terminal voltage.

The two-stage sweeping process (coarse sweeping plus fine sweeping) canbe performed faster than the single stage fine sweeping process. Thecoarse sweeping process for the nested loop effectively locates the“neighborhood” (e.g., data point 890A) of the optimum data point. Thecoarse sweeping process can be performed in a short amount of time dueto the relatively big step sizes. Thereafter, starting from this“neighborhood,” the fine sweeping process then locates the optimum datapoint. The fine sweeping process can also be performed in a short amountof time because, although the step sizes are smaller, the sweeping rangedoes not need to be very big. A small sweeping range along the Z-axiswill likely lead to an intersection with the target curve 860 andtherefore identify the optimum data point 895. Furthermore, the finesweeping process also saves time because it is a one-dimensional loop,as it does not need to be nested within an outer loop.

In an embodiment, the coarse sweeping process is sufficient to accountfor process variations such as lot to lot variations, wafer to wafervariations, and within-wafer variations. The fine sweeping process issufficient to account for within-die variations.

As discussed above, once the optimum supply voltage and the optimumdevice terminal voltage are identified—regardless of the specific methodused to identify them—they are used during the testing of testing unitsor DUTs. In an embodiment, to increase testing efficiency and speed, aparallel testing scheme is implemented. In parallel testing, multipletesting units are tested at the same time. These concurrently testedtesting units may be referred to as belonging to different sets. Eachset contains a plurality of testing units. All the testing units withinthe same set share the same testing pads. However, testing units fromdifferent sets may not share the same testing pads, or only share asubset of the testing pads.

For example, in an embodiment where four testing units are testedconcurrently, there are four sets of testing units. For ease ofreference, these four sets may be referred to as set A, set B, set C,and set D. In an embodiment, testing units in sets A, B, C, D may eachhave its own dedicated testing pads, including terminal testing pads andpower supply testing pads. In other words, the sets A, B, C, D arecompletely independent of one another. In that case, the testing of eachset can be carried out in the manner described above, for example usinga multi-dimensional sweeping process, which may include a coarsesweeping process followed by a fine sweeping process. An optimum supplyvoltage and an optimum device terminal voltage may be separatelyidentified and used for each of the four sets A, B, C, and D, since eachset may have its own optimum data point corresponding to the lowestleakage current.

In another embodiment, the four sets may share a subset of the testingpads such as power supply testing pads (e.g., testing pad for VDD). Thismay be done in the interest of conserving valuable chip area. In thatcase, the optimum supply voltage obtained by the coarse sweeping processmay be shared for all four sets. Stated differently, one of the sets maybe picked to run the coarse sweeping process so as to find the optimumsupply voltage. Once found, this supply voltage will be used to run thefine sweeping process for each of the four sets, where the fine sweepingprocesses are performed independently and therefore may yield somewhatdifferent optimum device terminal voltages.

Since the multi-dimensional sweeping process discussed above cansubstantially reduce electrical noise such as leakage current, a bettersignal-to-noise (S/N) ratio can be obtained. This is illustrated inFIGS. 15A and 15B, wherein FIG. 15A illustrates a graph 900 that is abox plot of S/N performance corresponding to conventional testingmethods, and wherein FIG. 15B illustrates a graph 910 that is a box plotof S/N performance corresponding to the multi-dimensional testing methoddiscussed above. An X-axis of the graphs 900-910 represents resistance,and a Y-axis of the graphs 900-910 represents S/N ratio. Resistors areused as testing units herein.

Referring to FIG. 15A, the graph 900 contains a plurality of lines 920that extend vertically along the Y-axis. Each line 920 represents aperformance of S/N at a particular resistance range. Collectively, theselines 920 span a plurality of resistance values and S/N ratios. Due tothe presence of electrical noise (such as leakage current), the S/Nratio is degraded. Suppose the minimum required S/N is 100, it can beseen that many of the lines 920 corresponding to resistances less thanabout 10,000 ohms drop below the S/N ratio of 100. One of the lines 920corresponding to a resistance value of about 60,000 ohms fails the S/Nrequirement of 100 entirely. Thus, many of the resistors will not passtesting. This is unfortunate because in actuality, some of theseresistors may have passing true S/N performance, but the S/N measurementis clouded or “contaminated” by the leakage current noise. As a result,such resistors (especially ones who are marginally passing the S/Nrequirement) may end up failing the S/N test. It may be difficult toascertain which of the resistors indeed have failing S/N ratios becausetheir S/N performances are not good, or which of the resistors onlyappear to have failing S/N ratios due to measurement inaccuracy causedby leakage current. Hence, some good resistors may be unnecessarilydiscarded.

In comparison, the graph 910 is compiled using the multi-dimensionaltesting method discussed above. Hence, leakage current is substantiallyreduced, which improves measurement accuracy. As a result, S/N ratio issubstantially improved. Among its lines 930, only one of which(corresponding to a resistance of about 70,000 ohms) is actuallydropping into the failing S/N territory of S/N<100. The rest of thelines 730 all have passing S/N performance. Therefore, it can be seenthat the multi-dimensional sweeping process improves test measurementaccuracy by minimizing leakage current.

It is understood that the multi-dimensional process discussed above maybe applied to a variety of testing units. For example, in theembodiments discussed above, a resistor is used as a testing unit, wherethe variables for the multi-dimensional loop include the supply voltage(VDD) and the device terminal voltage (voltage forced at a terminal ofthe resistor device). In alternative embodiments, a transistor such as aFET device may be used as a testing unit, where the variables for themulti-dimensional loop may include a supply voltage (VDD) and asubstrate bias voltage (voltage forced at a substrate terminal of theFET device). In is envisioned that alternative devices and theircorresponding variables may be used for other embodiments.

FIG. 16 is a flowchart that illustrates a method 950 for testing asemiconductor device according to various aspects of the presentdisclosure. The method 950 includes block 960, in which a test unit andan electronic circuit are provided. The electronic circuit iselectrically coupled to the test unit. The method 950 includes block970, in which a multi-dimensional sweeping process is performed. Themulti-dimensional sweeping process includes sweeping a plurality ofdifferent electrical parameters across their respective ranges. Themethod 950 includes block 980, in which a performance of the electroniccircuit during the multi-dimensional sweeping process is monitored. Themonitoring includes identifying optimum values of the differentelectrical parameters that yield a satisfactory performance of theelectronic circuit. The method 950 includes block 990, in which the testunit is tested using the optimum values of the different electricalparameters.

FIG. 17 is a block diagram of a computer system 1000 suitable forimplementing the various methods and devices described herein, forexample, the various method blocks of the method 500 in FIG. 9, themethod 700 in FIG. 12, and the method 950 in FIG. 16. In variousimplementations, the computer system 100 includes network communicationsdevices (e.g., servers, laptops, personal computers, etc.) capable ofcommunicating with a network.

In accordance with various embodiments of the present disclosure, thecomputer system 1000 includes a bus component 1002 or othercommunication mechanisms for communicating information, whichinterconnects subsystems and components, such as processing component1004 (e.g., processor, micro-controller, digital signal processor (DSP),etc.), system memory component 1006 (e.g., RAM), static storagecomponent 1008 (e.g., ROM), disk drive component 1010 (e.g., magnetic oroptical), network interface component 1012 (e.g., modem or Ethernetcard), display component 1014 (e.g., cathode ray tube (CRT) or liquidcrystal display (LCD)), input component 1016 (e.g., keyboard), cursorcontrol component 1018 (e.g., mouse or trackball), and image capturecomponent 1020 (e.g., analog or digital camera). In one implementation,disk drive component 1010 may comprise a database having one or moredisk drive components.

In accordance with embodiments of the present disclosure, computersystem 1000 performs specific operations by processor 1004 executing oneor more sequences of one or more instructions contained in system memorycomponent 1006. Such instructions may be read into system memorycomponent 1006 from another computer readable medium, such as staticstorage component 1008 or disk drive component 1010. In otherembodiments, hard-wired circuitry may be used in place of (or incombination with) software instructions to implement the presentdisclosure.

Logic may be encoded in a computer readable medium, which may refer toany medium that participates in providing instructions to processor 1004for execution. Such a medium may take many forms, including but notlimited to, non-volatile media and volatile media. In one embodiment,the computer readable medium is non-transitory. In variousimplementations, non-volatile media includes optical or magnetic disks,such as disk drive component 1010, and volatile media includes dynamicmemory, such as system memory component 1006. In one aspect, data andinformation related to execution instructions may be transmitted tocomputer system 1000 via a transmission media, such as in the form ofacoustic or light waves, including those generated during radio wave andinfrared data communications. In various implementations, transmissionmedia may include coaxial cables, copper wire, and fiber optics,including wires that comprise bus 1002.

Some common forms of computer readable media includes, for example,floppy disk, flexible disk, hard disk, magnetic tape, any other magneticmedium, CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, RAM, PROM, EPROM,FLASH-EPROM, any other memory chip or cartridge, carrier wave, or anyother medium from which a computer is adapted to read.

In various embodiments of the present disclosure, execution ofinstruction sequences to practice the present disclosure may beperformed by computer system 1000. In various other embodiments of thepresent disclosure, a plurality of computer systems 1000 coupled bycommunication link 1030 (e.g., a communications network, such as a LAN,WLAN, PTSN, and/or various other wired or wireless networks, includingtelecommunications, mobile, and cellular phone networks) may performinstruction sequences to practice the present disclosure in coordinationwith one another.

Computer system 1000 may transmit and receive messages, data,information and instructions, including one or more programs (i.e.,application code) through communication link 1030 and communicationinterface 1012. Received program code may be executed by processor 1004as received and/or stored in disk drive component 1010 or some othernon-volatile storage component for execution.

Where applicable, various embodiments provided by the present disclosuremay be implemented using hardware, software, or combinations of hardwareand software. Also, where applicable, the various hardware componentsand/or software components set forth herein may be combined intocomposite components comprising software, hardware, and/or both withoutdeparting from the spirit of the present disclosure. Where applicable,the various hardware components and/or software components set forthherein may be separated into sub-components comprising software,hardware, or both without departing from the scope of the presentdisclosure. In addition, where applicable, it is contemplated thatsoftware components may be implemented as hardware components andvice-versa.

Software, in accordance with the present disclosure, such as computerprogram code and/or data, may be stored on one or more computer readablemediums. It is also contemplated that software identified herein may beimplemented using one or more general purpose or specific purposecomputers and/or computer systems, networked and/or otherwise. Whereapplicable, the ordering of various steps described herein may bechanged, combined into composite steps, and/or separated into sub-stepsto provide features described herein.

The embodiments disclosed herein offer advantages over existing testingapparatuses, it being understood that other embodiments may offerdifferent advantages, and that no particular advantage is required forall embodiments. One advantage is the reduction of the number of testingpads. This is because the testing pads can now be “shared” by all thetesting units in a time-divided manner. Typically, the testing pads takeup much more room in a test line than the testing units, the controlcircuit, or the switching circuit. In other words, the implementation ofthe switching circuit, the control circuit, and/or extra testing unitsmay not consume much chip area. In comparison, the reduction in thenumber of testing pads (for example from at twenty-one testing pads downto twelve) results in significant savings in chip area consumption,which may lead to lower fabrication costs.

In addition, the embodiments disclosed herein can handle a greaternumber of testing units than existing test lines. As discussed above,existing test lines may require more and more testing pads as the numberof testing units continue to increase, which is the trend of modernsemiconductor fabrication. At some point, the traditional test line mayrun out of space and may not be able to handle the additional testingunits. Here, the number of testing pads can stay below a relatively lownumber, regardless of the number of testing units. As such, theembodiments disclosed herein are more adapted to handle the demands ofmodern (and future) semiconductor fabrication through its capability oftolerating an increasing number of testing units.

Furthermore, the embodiments disclosed herein are easy to implement andmay not require extra fabrication processes. The switching circuit andthe control circuit can be easily integrated into existing fabricationprocess flow.

Another advantage of the embodiments disclosed herein is the greatermeasurement accuracy it offers. The algorithms described above in FIG.12 (one-dimensional sweeping process) and FIG. 16 (multi-dimensionalsweeping process) may be used to identify an optimum value for a powersupply voltage and a device terminal voltage that correspond to aminimized electrical leakage current. Thus, overall background noise canbe reduced, and the device under test (DUT) can be measured moreaccurately during its testing. For example, the present disclosureallows current measurements down to the nano-amp level. In addition, theparallel testing configuration means that overall testing efficiency andspeed may be improved as well.

One of the broader forms of the present disclosure involves asemiconductor testing apparatus. The testing apparatus includes: aplurality of testing pads; a plurality of testing units; a switchingcircuit coupled between the testing pads and the testing units, theswitching circuit containing a plurality of switching devices; and acontrol circuit coupled to the switching circuit, the control circuitbeing operable to establish electrical coupling between a selectedtesting unit and one or more of the testing pads by selectivelyactivating a subset of the switching devices.

Another one of the broader forms of the present disclosure involves adevice for testing a semiconductor wafer. The device includes: aplurality of conductive test pads through which electrical signals canbe applied; a plurality of test structures each containing asemiconductor circuit component; routing circuitry containing aplurality of controllable switches that each include a control terminaland input/output terminals, wherein each switch is coupled between arespective one of the test pads and a respective one of the teststructures through its input/output terminals; and control circuitrycontaining a plurality of storage elements driven by a clock signal,wherein an output of each of the storage elements is coupled to arespective subset of the switches through their control terminals.

Another one of the broader forms of the present disclosure involves amethod for testing a semiconductor device. The method includes:providing a plurality of testing pads; providing a plurality of testingunits; providing a plurality of controllable switching devices that areeach coupled between a respective one of the testing pads and arespective one of the testing units; and selectively activating a subsetof the switching devices that are all coupled between a selected one ofthe testing units and at least a subset of the testing pads, wherein theselectively activating establishes electrical coupling between theselected testing unit and the subset of the testing pads.

Yet another one of the broader forms of the present disclosure involvesa method. The method includes: providing a testing unit and anelectronic circuit coupled to the testing unit; applying a firstelectrical signal to the testing unit; sweeping a second electricalsignal across a range of values, the second electrical signal supplyingpower to the electronic circuit, wherein the sweeping is performed whilea value of the first electrical signal remains substantially the same;measuring a third electrical signal during the sweeping, the measuredthird electrical signal having a range of values that each correspond toone of the values of the second electrical signal; adopting a value ofthe second electrical signal that yields a minimum value of the thirdelectrical signal as an optimum value of the second electrical signal;and testing the testing unit while the second electrical signal is setto the optimum value.

Another one of the broader forms of the present disclosure involves asemiconductor method. The method includes: providing a device under test(DUT), a plurality of testing pads, and electronic circuitry operable toestablish or cut off electrical coupling between the DUT and at least asubset of the testing pads; resetting circuit components in theelectronic circuitry; forcing a test voltage to a terminal of the DUT;applying a supply voltage to a power supply of the electronic circuitrywhile the test voltage is held at a constant value; detecting, inresponse to the applying, electrical noise generated by the electroniccircuitry; repeating the applying and the detecting a plurality of timesby adjusting an amount of the supply voltage for each repetition;identifying an amount of supply voltage that corresponds to a lowestamount of electrical noise as a target supply voltage; and thereaftertesting the DUT using target supply voltage.

One more of the broader forms of the present disclosure involves anapparatus comprising a non-transitory, tangible computer readablestorage medium storing a computer program. The computer program containsinstructions that when executed, perform: resetting a plurality ofcircuit components in an electronic circuit; maintaining a fixed voltageat a terminal of a device under test (DUT); making a plurality ofmeasurements with respect to electrical noise generated by theelectronic circuit, wherein each measurement is made by applying adifferent power supply voltage to the electronic circuit; anddetermining, in response to the making the plurality of measurements, anoptimum value of the power supply voltage that minimizes an amount ofelectrical noise.

Yet another one of the broader forms of the present disclosure involvesa method. The method includes: providing a test unit and an electroniccircuit that is electrically coupled to the test unit; performing amulti-dimensional sweeping process, wherein the multi-dimensionalsweeping process includes sweeping a plurality of different electricalparameters across their respective ranges; monitoring a performance ofthe electronic circuit during the multi-dimensional sweeping process,wherein the monitoring includes identifying optimum values of thedifferent electrical parameters that yield a satisfactory performance ofthe electronic circuit; and testing the test unit using the optimumvalues of the different electrical parameters.

Another one of the broader forms of the present disclosure involves asemiconductor testing method. The method includes: providing a deviceunder test (DUT), a plurality of testing pads, and electronic circuitryoperable to control electrical communication between the DUT and atleast a subset of the testing pads; applying a first voltage to the DUTand a second voltage to the electronic circuitry; detecting, in responseto the applying, electrical noise generated by the electronic circuitry;repeating the applying and the detecting a plurality of times bychanging values of the first and second voltages during each repetition;identifying target values of the first and second voltages thatcorrespond to a lowest amount of electrical noise; and testing the DUTusing the target values of the first and second voltages. In someembodiments, the first voltage includes a device terminal voltage andthe second voltage includes a power supply voltage.

In some embodiments, the repeating includes executing a nested loop thatincludes an inner loop and an outer loop, the inner loop being situatedwithin the outer loop, the inner loop includes a sweep of the firstvoltage, and the outer loop includes a sweep of the second voltage. Insome embodiments, the executing the nested loop yields the target valueof the second voltage. In such embodiments, the repeating can furtherincludes, after the nested loop is executed, performing an additionalsweep of the first voltage that yields the target value of the firstvoltage, the additional sweep being performed while the second voltageis maintained at the target value. In some embodiments, the DUT includesat least one of a resistor and a transistor, the electronic circuitryincludes a plurality of electronic switches and a plurality of memorystorage elements, and the electrical noise includes leakage current ofthe electronic circuitry. In some embodiments, the method furtherincludes executing one or more of the applying, the detecting, therepeating, the identifying, and the testing for a plurality ofadditional DUTs as a part of a parallel testing processes. In suchembodiments, at least a subset of the testing pads may be shared betweenthe DUT and the plurality of additional DUTs.

One more of the broader forms of the present disclosure involve anapparatus comprising a non-transitory, tangible computer readablestorage medium storing a computer program. The computer program containsinstructions that when executed, perform: performing a first sweepingprocess with respect to a first electrical parameter and a secondelectrical parameter, the sweeping process being performed on a testingunit and an electronic circuit communicatively coupled to the testingunit; determining a first optimum value of the first electricalparameter in response to the first sweeping process, the first optimumvalue being a value that yields a lower electrical noise than othervalues of the first electrical parameter; thereafter performing a secondsweeping process with respect to the second electrical parameter, thesecond sweeping process being performed while the first electricalparameter is maintained at the first optimum value; determining a secondoptimum value of the second electrical parameter in response to thesecond sweeping process, the second optimum value being a value thatyields a lower electrical noise than other values of the secondelectrical parameter; and testing the testing unit using the first andsecond optimum values for the first and second electrical parameters,respectively. In some embodiments, the first sweeping process is carriedout using greater sweeping steps than the second sweeping process.

In some embodiments, the first electrical parameter includes a powersupply voltage, the second electrical parameter includes a deviceterminal voltage, and the first sweeping process is executed using anested loop, the device terminal voltage being a variable of an innerloop of the nested loop, and the power supply voltage being a variableof an outer loop of the nested loop. In some embodiments, the electroniccircuit contains a plurality of electronic switching devices that areoperable to selectively establish communication between the testing unitand a plurality of testing pads. In such embodiments, the instructionsfor performing the first sweeping process and the instructions forperforming the second sweeping process each contain instructions fordeactivating at least a subset of the electronic switching devices, andthe instructions for testing the testing unit contain instructions foractivating at least a subset of the electronic switching devices.

Yet another one of the broader forms of the present disclosure involvesa method. The method includes providing a device-under-test electricallycoupled to a testing apparatus; and determining an optimum value of afirst electrical parameter and an optimum value of a second parameter bytesting the device-under-test according to a set of first electricalparameter values and a set of second electrical parameter values. Theoptimum value of the first electrical parameter and the optimum value ofthe second parameter are determined based on an electrical noiseresponse of the device-under-test. In some embodiments, the firstparameter corresponds to a supply voltage and the second parametercorresponds to a device terminal voltage. In some embodiments, theoptimum value of the first electrical parameter and the optimum value ofthe second parameter are determined using a first set of contacts of thedevice-under-test. In such embodiments, the method can further includetesting the device-under test using a second set of contacts of thedevice-under-test according to at least one of the optimum value of thefirst electrical parameter or the optimum value of the second parameter.In some embodiments, the values of the set of first electrical parametervalues are at a coarser interval than the values of the set of secondelectrical parameter values.

Yet another one of the broader forms of the present disclosure involvesa method. The method includes electrically coupling a plurality oftesting pads of a circuit to test unit and iteratively testing thecircuit using the test unit according to a first parameter and a secondparameter. The first parameter is tested at each of a first plurality ofsteps within a first range, and the second parameter is tested at eachof a second plurality of steps within a second range. The testing of thecircuit is performed to determine a response at each combination of thefirst plurality of steps and the second plurality of steps byiteratively selecting one of the first plurality of steps and testingthe circuit using each step of the second plurality of steps. In someembodiments, the first parameter corresponds to a first voltage and thesecond parameter corresponds to a second voltage. In some embodiments,the first parameter corresponds to a supply voltage and the secondparameter corresponds to a device terminal voltage. In some embodiments,the first plurality of steps is at a coarser interval than the firstplurality of steps. In some embodiments, the response includes a leakagecurrent.

In some embodiments, the method further includes determining one of thefirst plurality of steps as an optimum value of the first parameterbased on the corresponding determined response, and determining one ofthe second plurality of steps as an optimum value of the secondparameter based on the corresponding determined response. In someembodiments, the testing of the circuit is performed using a first padset of the plurality of testing pads. In such embodiments, the methodcan further include iteratively testing the circuit using a second padset of the plurality of testing pads according to at least one of theoptimum value of the first parameter or the optimum value of the secondparameter.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: providing adevice-under-test electrically coupled to a testing apparatus; applyinga set of first electrical parameter values to the testing apparatus;applying a set of second electrical parameter values to thedevice-under-test; monitoring an electrical noise response of thetesting apparatus during the applying the set of the first electricalparameter values and the set of the second electrical parameter values;determining a selected first electrical parameter value from the set ofthe first electrical parameter values corresponding to each of the setof the second electrical parameter values that minimize the electricalnoise response of the testing apparatus when applying the correspondingeach of the set of second electrical parameter value; comparing theminimum electrical noise response for each of the selected firstelectrical parameter values corresponding to each of the set of thesecond electrical parameter values to determine an optimum firstelectrical parameter value from the selected first electrical parametervalues that generate a least electrical noise response of the testingapparatus; determining the second electrical parameter valuecorresponding to the optimum first electrical parameter as an optimumsecond electrical parameter value from the set of the second electricalparameter values; and evaluating performance of the device-under-testusing the optimum first electrical parameter value and the optimumsecond electrical parameter value.
 2. The method of claim 1, wherein theoptimum first electrical parameter value is a supply voltage and theoptimum second electrical parameter value is a device terminal voltage.3. The method of claim 1, wherein the optimum first electrical parametervalue and the optimum second electrical parameter value are determinedusing a first set of contacts of the device-under-test, and thedevice-under-test is evaluated using a second set of contacts of thedevice-under-test according to at least one of the optimum firstelectrical parameter value or the optimum second electrical parametervalue.
 4. The method of claim 1, wherein the values of the set of firstelectrical parameter values are at a coarser interval than the values ofthe set of second electrical parameter values.
 5. The method of claim 1,wherein the determining the selected first electrical parameter valuefrom the set of the first electrical parameter values corresponding toeach of the set of the second electrical parameter values includes:applying a fixed second electrical parameter value to thedevice-under-test while applying each of the set of first electricalparameter values to the testing apparatus.
 6. The method of claim 5,wherein the determining the selected first electrical parameter valuecorresponding to the fixed second electrical parameter values includes:measuring the electrical noise response of the testing apparatus whenapplying the fixed second electrical parameter values to thedevice-under-test while applying each of the set of first electricalparameter values to the testing apparatus.
 7. The method of claim 5,wherein wherein the determining the selected first electrical parametervalue corresponding to the fixed second electrical parameter valuesincludes: comparing the electrical noise response of the testingapparatus when applying the fixed second electrical parameter values tothe device-under-test while applying each of the set of first electricalparameter values to the testing apparatus to decide the minimumelectrical noise response; and determine the selected first electricalparameter value from the set of first electrical parameter values thatgenerate the minimum electrical noise response corresponding to thefixed second electrical parameter value of the set of the secondelectrical parameter values.